Nuclear fuel compositions and method of making the same



. NUCLEAR 3,102,848 FUEL COMPOSITIONS AND METHOD I OFMAKINGTHESAME Menahem Merluh-Sobel, Jersey City, N.J., assignor to Curtiss-Wright Corporation, a corporation of Delaware No Drawing Filed Nov. 23, 1959, Ser. No. 854,531

. a 1 Claim. (Cl. 204-4542) This invention relates to improved fuel compositions for nuclear reactors, and more particularly to mixtures of uranium dioxide with molybdenum or tungsten, in which the components are evenly distributed and intimately mixed on a molecular level, and to the method oi making such compositions. i

i In the prior art of making nuclear fuel compositions,

PatentedSept. 3, 1963 2 M salt, Z is either tungsten or molybdenum, 0 is oxygen in the required amount, and L is any ion capable of forming a soluble salt with and with T.

Thereduction reaction proceeds according to the general equation w i l MZO,,+Q MO+Z+J where, Q is a reducing agent of the class specified above, and I is one or more volatile oxides. For the purposes of my invention water is considered a volatile. oxide. The resultant compositionof MO-i-Z is a combination of particles or molecular size of uranium dioxide with tungsten or molybdenum, intimately mixed andidispersed at the or fiuel elements as they are frequently termed, it is I known to make pellets, cubes, or other shapes. of oompressed powdered uranium dioxide and powdered metal,

such as molybdenum or tungsten. The uranium of which the oxide is made is more or less highly enriched in its content of uranium-235, according to the degree {of nuclear activity desired and thewamountof the free metal to be it mixed with the oxide. Such compositions are useful in providing more efficient retention of fission products by partial alloying between the free metal and the fission products. p I

However, prior to the present invention it has been necessary to make the compositions" of ground uranium dioxide and ground metal, with 'a resultant limitation on the tungsten or molybdenum, may be in particles as large as It is highly desirable that such nuclear fuel compositions be made of particles of the smallest possible size, both in order tosecure a greater intimacy of mix and more even dispersion, and also [for the added advantage of better dissipation of'heatthrough the free metal cornponent.

' be readily understood on reading the following specification.

V I have found that an intimatemix of uranium dioxide with either tungsten or molybdenum canbe made, having particles of molecular size, by reacting a soluble salt of uranium with a soluble salt of either tungsten or molybdenum to form an insoluble salt containing uranium, oxygen, and one of the other two metals, and reducing this compound by a reducing agent which forms a volatile oxide. Examples of such reducing agents are (hydrogen, hydrocarbons, or carbon. Uranium dioxide is not reducible by such an agent, Whereas both tungsten and molybdenum are reducible by this means. Uranium salts of an acidic oxide, such as uranyl nitrate, for example, are preferred as starting points, although uranium halides or uranyl halides or other salts maybe used. l

The general equation for the first reaction is as follows:

' MT+LZO,,- lMZo -l-LT where M is a uranium containing ion, T is the anion of an molecular level, and suitable for pressing and sintering by well-known methods to form pellets or other shapes for nuclear fuel elements.

Following are idealized equations for specific nuclear fuel compositions made 'according to my invention.

u Example I u 1 U0 N0 2 +K WO tUO WO +2KNO UO WO 4H UO +W+4H O Although in this example uranyl, nitrate is given as one of. the starting compounds, it will be understood that according to the general equation another soluble uranium salt may be used, such as any of the uranium chlorides or sulfates, for example. Similarly, in place of potassium tungstate I may use any soluble tungstate of which the cation forms a soluble salt with the anion of the uranium salt selected, such as annnoniumtungstate.

Example I1 I v UO CI (N11 Mo04 iUO Mo O +Z(NH;,) Cl

UO MoO +C UO +Mo+4CO Equivalents apply in this example as in Example I.

Example 111 V UO Cl (NH WO.,- tUO WO +2NH C Again, in place of uranyl chloride I may use any soluble salt of uranium, and instead of ammonium tun gstate I may use any soluble tungstate of which thecation forms a soluble salt with the anion Otf the selected uranium compound. r

Example IV UOg(NO +Na MoO iUO5MoO +2NaNO UO2M0O4+ 02 Mo'fl' Thesame equivalents apply in this example as in EX- amples I, II, andlII, according 'to the general equation.

reducing agents, higher hydrocarbons may be used. When using carbon, particular care must be taken to provide stoichiometric amounts and to control the reaction, in order that no undesirable carbon residue may remain in the product. It will be understood that in the reduction phase of the process, the reduction reaction is carried out according to well-known techniques, and that it must be at a temperature not less than that required for the complete reduction of tungsten or molybdenum, that is, approximately l 000 F. l l i It is also apparent that in the idealized equations given above, the insoluble precipitate of the first reaction of each example may not always be [a true compound as shown, but may contain hydrates or hydroxides. This does not affect the chemistry of the procedure, since suchcompounds are reducible by the same agents in the same manner.

It may sometimes be desirable to adjust the proportions of the nuclear fuel compositions to contain more or less uranium dioxide or of the tree metal. This can be accommetal and remove the anionf n'the filtrate. The following equations will exemplify thisreaction.

; neously, and are treated with the reducing agent; to leave afuel composition having a double proportion of tungsten to uraniumjdioxide. It will be obvious that any desired Proportion of the two components of the fuel composition 1 can be achieved !by adjusting the proportions of the starting salts.' 1 I Although I havedescribed my invention above in a pre- ',ferred torm, it will be understood by those skilled in the artmllat various changes and modifications may be made withoutdeparting from the scope of the invention. It is intended 'to oover'all such modifications by he appended claim.

What is claimed is:

' The pr cess of making nuclear tfiuel compositions, comprising reacting an aqueous solution of a first salt selected firom the group consisting of urany-l nitrate, uranyl '01110- 1 ride, uraniumchloride, and uranium'sulfate witli-anaqueous solution of a second salt selected from the gnoup consisting of ammonium 'molybdate, potassium molybd'ate sodium molybdate, ammonium tungstate, potassium tungstate, and sodium tungstate, each of said second salts havimg an anion which forms an insoluble precipitate "with the cations of the members of said first group, and reducing said precipitate by a reducing agent selected fnom the group consisting oifhydrogen, methane, and carbon at a temperature of at least 1000 F. to form a nuclearfuel lcomposition consisting :of uranium dioxide in a molecular mix with the metal of rth'ewanionioifsaid selected second salt References Cited in the file of this patent a UNITED srA rEsi PATENTS d 9:93.,270. Nieske'et a1. May 23, .1911 2,012,825 Millner et a1 Aug. 27, 1935 2,848,391 Fehnoe et a1 Aug. 19, 1958 9 2,860,098 Fahnoe etal ,Nov.-11, 19-58 2,893,859;- Trifflemlan July 7, 1959 2,972,529 A-lexander et al Feb.-21, 1961 3,019,103 Alexander et al Jan. 30, 1962 FOREIGN PATENTS Great Britain Dec. 23,1957

OTHER REFERENCES 7 Peaceful Usesof Atomic Energy, vol. 9, published by the United Nations, 1956, Weber et al., DispersionType Fuel Elements, pp. 198 and 1 99 relied upon.

Nuclear Fuels, publishedby D. Van Nostrand Co. Inc,

19516, p. 279 relied upon. 7 

